I. Field of the Invention
This invention relates to an optical scanner for scanning light signals, such as light beams. More particularly, this invention relates to an optical scanner with an electrostrictive element or, in particular, a piezoelectric element for generating a modification by applying a voltage. It is mainly used, for example, as a device for conducting light beams to a predetermined position of a photosensitive material of a laser beam printer and further used for various portable and battery-operated optical apparatuses.
II. Description of the Prior Art
In a conventional optical scanner, a polygon mirror is rotated by an electric motor, the conventional optical scanner needs a shock-absorbing device for eliminating the vibration accompanied with motor driving as well as a mechanism for rotating the polygon mirror. Consequently, the mechanism not only becomes complicated, but also the total volume and weight thereof become bigger. The conventional optical scanner is not suitable for various portable apparatuses which need a little electric power.
To solve these problems, Japanese Examined Published Patent Application No. 52-40215, Japanese Unexamined Published Patent Applications No. 60-177316 and No. 61-132919 disclose light deflecting apparatuses using a bimorph type piezoelectric element or a multilayer type piezoelectric element.
In the apparatus with the bimorph type piezoelectric element, one end of the piezoelectric element is fixed and the other end is connected to a lower part on the periphery of a reflecting mirror to support the mirror and to incline the mirror when the piezoelectric element is modified and bent by applying a voltage.
In the apparatus with the multilayer piezoelectric element, a supporting plate for a mirror is provided at its upper surface with the mirror surface, and the plate is vacillatingly attached to one point as a fulcrum. Modifiable ends of two multilayer type piezoelectric elements, which expand and contract upwardly and downwardly, are connected to the lower surface of the supporting plate through a flexible and elastic driving member at two positions. The two positions are separated from the fulcrum and are located on a plane including both an X-axis and a Y-axis that pass the fulcrum and cross at right angle to each other.
In this apparatus, when the piezoelectric elements are given a different volume or a different time of expanding or contracting each other by changing voltages applied thereto, the driving member acts as lever and drives the reflecting mirror to incline along various angles according to the applied voltages to thereby generate plural vacillations. As a result, the reflecting mirror can rapidly deflect incident light signals to an arbitrary direction.
Since each of reflecting mirrors of the conventional apparatuses is a heavy flat mirror, the former apparatus is defective in strength and in that its deflecting angle is comparatively small. Since the reflecting mirror of the latter apparatus is driven by the multilayer type actuator and the modified volume of the supporting plate is not big without using a lever such as the driving member, the latter apparatus is defective in that a large deflecting angle cannot be obtained without a complicated mechanism.